WO1991003685A1 - Process and installation for the combustion of oxygen-free toxic gas effluents - Google Patents

Abstract

Process for the combustion of oxygen-free toxic gaseous effluents in a flame, including an inner cone (8) supplied with combustible gas (6) and with a so-called primary oxidant gas (7). Said effluent gas (10) and a so-called secondary oxidant gas (9) are introduced separately at the level of the inner cone. The secondary oxidant gas is introduced in the form of at least one jet directed at the axis (D) of the inner cone at a flow rate and speed which are sufficient to ensure an excess of oxidant, as well as maintaining the temperature, and creating a turbulent gaseous mass at the level of the inner cone. The toxic gas effluent (10) is then introduced into the resulting turbulent gaseous mass. The invention also relates to an installation for the implementation of said process, which takes place at negative pressure.

Description

Process and installation for the combustion of toxic gaseous effluents devoid of oxygen.

The invention relates to a method and an installation for the destruction by combustion of toxic oxygen-free gaseous effluents.

The problem of eliminating such effluents has arisen in particular in integrated circuit manufacturing units where, to boost materials, gases loaded with arsenic hydrides (arsines), and / or phosphorus hydrides ( phosphines) and / or siLiciu hydrides (siLanes) ...

These gases are toxic and the gas stream containing them must absolutely be purified before being released into the atmosphere. A known treatment method consists in burning

Said gases; The combustion products are not toxic or can be easily eliminated (for example by filtration for arsenious oxide).

The patent FR 87 03 729 published under the number 2 612 606 describes such a process with its associated device. According to this patent, the effluent is brought into a combustion zone by a central duct surrounded by a tube bringing the combustible gas, itself surrounded by three annular conduits bringing the combustion air. We strive to remain as long as possible in the laminar flux beyond the burner to repel the area of ignition in order to avoid the deposition of oxides on the burner. The gas injection rates and speeds are adjusted for this purpose. For the same purpose, the combustible gas stream constitutes a protective sheath for the effluent vis-à-vis the oxidizing gas. The Applicant currently offers a combustion process in which, unlike the prior art, significant turbulence is created.

More precisely. The subject of the invention is a process for the combustion of toxic gaseous effluents devoid of oxygen in a flame comprising a dart supplied with combustible gas and in so-called primary oxidizing gas, process implemented in vacuum and in which said gaseous effluent and a so-called secondary oxidizing gas are introduced separately at said dart, said secondary oxidizing gas being introduced in the form of at least one jet directed towards the axis of said dart at a rate and speed sufficient to ensure an excess by oxidizing. Maintaining the temperature and creating a turbulent gas mass at the level of said dart; The toxic gaseous effLuent being introduced into said turbulent gaseous mass. The invention therefore consists of a process for combustion of toxic gaseous effluents, devoid of oxygen. Such effluent is not, in itself, exposible. They can become so in the presence of oxygen.

They consist of a carrier gas loaded with impurities. Said carrier gas can be Hydrogen, Nitrogen, or a mixture of gases. Air and oxygen are obviously excluded.

Said gaseous effluents to be burned according to the process of the invention can, as indicated above, come from the electronic industry. Such effluent is loaded with hydride, in particular phosphines, arsines "and / or si Lanes ... and / or other chemical compounds containing in particular atoms B, P, As, Te, Se, CL, F.

Said gaseous effluents can also come from the nuclear industry. It can be pyroLysis gas and / or radioactive gas loaded with tritium.

The stinger is obtained from a conventional burner placed at the head of the combustion zone, supplied with combustible gas (natural gas for example) and oxidizing gas (air for example). This oxidizing gas is called primary in the text of the present application to distinguish it from the other oxidizing currents. Advantageously, the flow rate of this primary oxidizing gas is adjusted so as to ensure combustion, with a small excess of oxidizing gas (approximately 10%).

According to the invention, so-called secondary oxidizing gas is sent to the dart in the form of a jet (s), at a rate sufficient to ensure an excess of oxidizer, relative to the quantity necessary for the combustion of the toxic effluent, and at a speed sufficient to create a turbulent gas mass at the level of the stinger.

The secondary oxidizing gas is, for example, air. The flow rate and the speed of the secondary oxidizing gas are such that the appearance of the sting is modified: it changes color, its shape is disturbed and we observe perverse movements. It is said then that the gas mass is turbulent. This phenomenon is known to those skilled in the art. The flow rate and speed of the secondary oxidant gas must also be determined to ensure temperature maintenance in the combustion zone and excess oxidant.

The speeds can go up to several tens of m / s. The secondary oxidizing gas is introduced in the form of one or more jets directed towards the axis of said dart. These jets can converge towards the axis of the dart or else be directed so as to create a peat LLonnai re movement of the oxidizer around said dart; in this case also, the orientation of the jet contributes to the creation of turbulence.

The method of the invention is implemented, under vacuum with respect to the atmosphere outside the combustion zone (ambient atmosphere). Such a depression prevents the formation of gas pockets, avoids possible dispersion of the gases to the outside. IT IS EASY BY ELSEWHERE The extraction of gases from the installation in which the process is implemented.

This depression is of the order of 0.5 to 6 mbar (or 50 to 600 Pa). Preferably. The secondary oxidizing gas is brought in by two different circuits producing:

- At least one so-called fixed jet with a constant flow and speed sufficient to obtain a turbulent gas mass, and the desired combustion temperature; - at least one jet called modulable with a variable flow to maintain the temperature; Said jets also ensuring the supply of excess oxidant.

The modulable (secondary) oxidant gas stream cools the gas mass and allows the temperature of the combustion zone to be lowered, if necessary. By the absence of said current, the temperature rises, which can be accelerated by adjusting the flow rate of combustible gas / primary oxidant.

It is sufficient, within the framework of the invention, for the toxic gaseous effluent to be introduced in the form of a jet into the turbulent gas mass (one or more jets). Regardless of where the effluent jet (s) arrives (s) in relation to the arrival of secondary oxidant gas, it is sufficient that turbulence is created on the gas mass . When the toxic effluent is of a different nature, it can be introduced in the form of separate jets at the level of the stinger, or else it can be mixed before being introduced.

The toxic effLuent can be introduced occasionally. The flow of secondary oxidant gas is generally controlled by the measurement of the temperature in the combustion zone. The method of the invention makes it possible, advantageously, to treat effLuents whose flow and speed are not controlled; It is enough then to regulate the flow rates and speeds of oxidizing gas to result in combustion. The temperature in the combustion zone is generally higher than 900 C for the treatment of the aforementioned toxic gases. Said temperature is advantageously chosen so as to obtain at least 99% destruction of the toxic gases over the whole of the installation - that is to say, a possible complete combustion zone of a post-combustion zone. in LaqueLLe the reaction ends- in LaqueLLe The process of the invention is implemented.

In any case, it will be chosen, by a person skilled in the art, above a critical temperature: The temperature of explosion of the gas mixture in the combustion zone. What that said mixture, the skilled person locates around

800 ° C this critical temperature.

In the absence of effluent to be treated, it is advantageous to standby at a temperature very slightly higher than the temperature of explosion of the gases then present in the combustion zone.

To allow the combustion reaction to extend, it is advantageous to send the gases from the combustion zone to a so-called post-combustion zone containing a lining of refractory materials. Said lining is advantageously brought to a temperature above the combustion temperature in the combustion zone. Said lining also ensures gas filtration and better distribution of calories in the installation. Said post-combustion zone is obviously, too, in depression (0.5 to 6 mbar preferably).

It may be wise to cause a leak in the top of the post-combustion zone (part opposite to the bottom containing the lining) leading to a slight stream of so-called tertiary oxidant gas (air in general ⁾ which guarantees an excess of oxidant in the zone post-combustion.

The flow rates and speeds of the oxidizing gases are regulated so as to obtain a temperature of 900 to 1,200 ° C., approximately 1,000 ° C., in the post-combustion zone, within the framework of an application to the toxic effluents listed above. above.

The gases leaving can be discharged directly into the atmosphere or be treated, depending on the quantity of toxic residues and the standards of discharge in force.

The present invention also relates to an installation for the combustion of toxic gaseous effluents devoid of oxygen, in which the process described above can be implemented. Said installation comprises:

- a tunneL or combustion zone, the bottom of which consists of a conical wall open on said tunneL and of the same axis as Him; a burner supplied with combustible gas and gas primary oxidant being disposed on this axis so that the base of the dart is located near the bottom of the tunnel,

- at least one tube to bring the secondary oxidant gas to the bottom of said tunnel, the (said) tube (s) being oriented (s) so that said oxidant gas is directed in jet (s) towards the dart ,

- at least one tubing to bring the toxic gaseous effluent to the bottom of said tunnel, the so-called tubing (s) being oriented so that the effLuent is directed in convergent jet (s) ( s) towards the axis of the da rd.

- a gas extraction device, creating a depression in said tunneL.

The installation according to the invention comprises a combustion tunnel, the bottom of which consists of a conical wall. This wall is generally made up of refractory materials over a thickness sufficient to ensure the thermal insulation of

The facility vis-à-vis the outside.

In the bottom of the cone is a recess for the burner. The burner includes a pipe for the supply of combustible gas and another pipe for the supply of primary oxidizing gas.

It could for example be a workman spared at the bottom of the tunnel, in which the burner opens, the dart developing then in the workman. In another embodiment, the burner comprises two concentric tubes, and the tube bringing the fuel is placed back from the bottom of the tunnel cone, in order to facilitate the primary fuel / oxidizer mixture before the development of the dart, the base of the dart being practically at the bottom of the cone of the combustion tunnel.

Flow control means are provided on these pipes; they are preferably bonded to the measurement of the temperature in ¹ L installation.

On the conical wall of the combustion tunnel, come the secondary oxidant gas and toxic effluent. The secondary oxidant gas is supplied by one or more tubes which pass through the conical wall over its entire thickness. The tubes are dimensioned so that the gas escapes in the form of a jet. These tubes can be given a slit shape so as to cover the jets with a larger surface.

A more favorable embodiment consists of providing several pipes, for example three or four, regularly arranged around the circumference of the conical wall. As the case may be, the tubes are arranged so that the jets converge towards the axis of the dart substantially at the same point, or else they are identically inclined around the periphery of the conical wall so as to create a rotary movement of the oxidant gas introduced. .

The tubing (s ⁾ bringing the effluent, also crosses the conical wall and is (are) arranged so as to direct the jet (s) of effluent towards the axis of the dart sensibly at the same point. Preferably, several pipes are regularly distributed around the periphery of the conical wall.

Preferably, provision is made of secondary oxidant gas pipes for so-called fixed jets and pipes for said modular jets, each type of jet being pi Loted independently of the other.

In a particular embodiment, there are provided tubes separated into two parts by a wall, the jets then opening substantially in the same place.

The dimensions of the combustion tunnel are determined by a person skilled in the art depending on the products treated, the combustion temperature to be obtained, the residence time, etc.

A device, for example an extraction fan, is mounted on the gas extraction pipe to create the vacuum in the installation.

An interesting installation comprises a combustion tunnel followed by a post-combustion zone, said zone also comprising refractory walls and its axis advantageously forming an angle with that of the combustion tunnel. The bottom of said zone is provided with a lining of refractory material and a lateral tube allows the outlet of the gases having passed through said lining.

In the top of the post-combustion zone (the top being opposite the bottom), an intake valve can be fitted, allowing the passage of oxidant (tertiary oxidant) to the bottom of said post-combustion zone. Advantageously, said valve is used as an expansion valve, to compensate for accidental overpressures. The figures below illustrate the invention:

- Figures 1A and 1B show preferred embodiments of the installation according to the invention;

- Figures 2A, 2B and 3A show in section (view along the axis of the combustion tunnel) The bottom of the tunnel with the burner and the gas pipes, Figure 3B shows a section view of

INSTALLATION 1B ACCORDING TO DIRECTION F.

FIG. 1A shows an installation comprising a combustion tunnel 1 of axis (D) followed by a post-combustion zone 2 disposed perpendicularly to said tunnel. The bottom of the tunneL 1 is constituted by a conical wall 3 open on the tunneL. The tunnel with its bottom is surrounded by a thickness 4 of refractory bricks (or other material) to ensure thermal insulation.

In the bottom of the tunnel, a recess is arranged along the axis (D) and over the entire thickness of the conical wall. A burner

5 is embedded therein, which comprises a line 6 for the arrival of combustible gas (natural gas) and a line 7 supplying the primary oxidizing gas (air). A dart 8 grows in the bottom of the tunnel. In FIG. 1A, the base of the stinger is at the bottom of the cone of

The conical wall; in FIG. 1B, it is located in the opening placed on the recess arranged in the bottom of the cone.

Tubes 9 and 10 pass through the conical wall to supply the secondary oxidizing gas (air) and the toxic effluent respectively. In the example illustrated in FIGS. 1A and 2A, three tubes 9 and three tubes 10. The tubes 9 are arranged so that their axes converge on the axis (D) of the tunnel at a point A, The tubes 10 in point B and point B is located beyond point A.

On the other hand, in FIG. 1B, the tubes 9 converge at points A1 and A2, the tubes 10 at point B and Points A1 and A2 are located beyond point B.

In the section in FIG. 2A, according to one embodiment of the invention, the pipes 9 supplying the secondary oxidizing gas have a slit shape while the pipes 10 have a recirculated shape.

FIG. 3A presents a preferred variant, in which the tubes 9 are separated into two parts by a partition 11. In part 12, the closest to the burner, circulates the secondary oxidizing gas with fixed jet and in part 13 the oxidizing gas. secondary with modular jet. The two parts are then supplied by different pipes. On the supply pipes, there are suitable means of regulating flow and speed.

FIG. 1B shows separate tubes 9A and 9B for supplying the secondary oxidizing gas in the form of a modulable and fixed jet respectively.

FIG. 2B shows in section Tubings 9B incined so as to create a rotary movement of the secondary oxidizing gas known as a fixed jet around the dart.

Tubing 10 is divided into three groups of three tubing 10A, 10B, 10C which each bring a toxic effluent of a different nature, for example. The group pipes are regularly arranged around the circumference of the conical wall.

According to Figure 1A, The gases from the combustion tunnel

1 are diverted towards the post-combustion zone 2 which contains at its bottom a lining 14 (in silicon carbide for example) which can be evacuated by a withdrawal door 15 and brought by a door 16. The door 16 may include a cLapet 17 by LequeL arrives then tertiary oxidant (air) which is entrained with the combustion gases towards the lining. The gases which have passed through the lining, leave the installation via the pipe 18.

The invention is illustrated by the example below. In an installation of the type described above, the cylindrical combustion chamber of which has an external diameter of approximately 1,200 mm, an internal diameter of approximately 400 mm, an approximate internal length of 1,600 mm and of which the post- combustion - which follows said combustion chamber - contains silicon carbide aggregates, a gas loaded with arsine, at 6000 ppm in volume, was treated at a flow rate of 14 Nm / h.

At the head and in the axis of the combustion tunnel, there is a burner flue supporting the burner itself and the air and gas inlets. The carrier gas loaded with arsine is sent in the quarry to the combustion tunnel. It is composed of :

- hydrogen 10.2 Nm / h

- nitrogen 3.0 Nm ³ / h

The fuel used is natural gas, delivered at a rate of 1.1 Nm / h at the nose of the burner, previously mixed in the burner at 6 Nm / h of primary air (primary oxidant). The air / gas ratio was kept constant, regardless of the burner flame size, with a 10% excess of air compared to stoichiometry. Through the burner outlet also arrives at a speed of 12 m / s The secondary oxidizing gas composed of:

- air at constant flow (33 Nm / h) and at constant speed (12 m / s) for turbulent sweeping of the combustion tunnel, - modulated air with variable flow (from 0 to 35 Nm / h) for

Maintaining temperature.

The depression in Tunisia is 5 mbar. The temperature measured before the silicon carbide packing is 1000 C. The volume of the fumes at this temperature is 90 Nm ³ / h. Said fumes are then cooled from 1000 C to 700 C in a heat exchanger and then undergo a dilution, by ambient air, of a factor of 4 (325 Nm / h ⁾ to be brought back to a temperature of 100-120 C before a very high efficiency filtration (to stop 99.99% of particles of the order of 0.3 μm) aimed at retaining the arsenious acid, solid, formed, before rejection to the chimney.

At this level, the arsine charge is no more than 0.5 ppm by volume. The purification yield provided by the installation is therefore 99.966%, higher than the 99.95% required (after taking into account the dilution on cooling).

In addition, the composition of the fumes at the chimney was approximately as follows:

- nitrogen 80.0% - oxygen 18.0%

- water (steam) 1.5%

- carbon dioxide 0.5%

Such an installation has gone completely well suited for the purification of gases from the electronic industry: not only is there virtually complete combustion of toxic combustible elements, but the formation of nitrogen oxides or other toxic gases is avoided.

Claims

1. Method for the combustion of toxic gaseous effluents devoid of oxygen in a flame, comprising a dart supplied with combustible gas and with so-called primary oxidizing gas, characterized in that it is used in depression and in that said gaseous effluent and a so-called secondary oxidizing gas are introduced separately at the level of said stinger. Said secondary oxidant gas being introduced in the form of at least one jet directed towards the axis of said dart at a rate and a speed sufficient to ensure an excess of oxidant, maintaining the temperature and creating a turbulent gas mass at the level of said dart; The toxic gaseous effLuent being introduced into said turbulent gaseous mass. 2. Method according to claim 1, characterized in that said secondary oxidizing gas is introduced - In the form of at least one so-called fixed jet, at a constant rate and speed and sufficient to obtain a turbulent gas mass and the desired combustion temperature; - And in the form of at least one so-called modulable jet, with variable flow, making it possible to stabilize said combustion temperature; Said jets also ensuring the supply of excess oxidant. 3. Method according to one of claims 1 or 2, characterized in that the flow of secondary oxidant gas is controlled by the measurement of the temperature in the combustion zone. 4. Method according to one of the preceding claims, characterized in that the gases from the combustion zone are sent to a post-combustion zone. 5. Method according to one of the preceding claims, characterized in that the combustion zone and the post-combustion zone, if any, are in depression of 50 to 600 Pa relative to the ambient atmosphere. 6. Method according to one of claims 4 or 5, characterized in that a stream of additional oxidant gas (called tertiary oxidant) is introduced into the gases from combustion zone, to guarantee in excess by oxidizing in the post-combustion zone. 7. Method according to one of claims 4 to 6, characterized in that there prevails in the post-combustion zone a temperature between 900 and 1,200 C, and preferably a temperature of about 1,000 C. 8. Method according to one of the preceding claims, characterized in that the treated effluent contains at least one of the following constituents: siLane, B, P, As, Te, Se, CL, F. 9. Installation for the combustion of toxic gaseous effluents devoid of oxygen by implementing the method according to any of the preceding claims. Said installation comprising a combustion tunnel (1) in the bottom of which is a burner (5), supplied with combustible gas and with so-called primary oxidizing gas, characterized in that: - The bottom of said tunneL (1) consists of a conical wall (3) open on said tunneL (1) and of the same axis (D) as Him; The burner (5) being disposed on this axis (D), so that the base of the dart is located near the bottom of said tunnel (1); and in that said installation further comprises: - at least one tube (9) for bringing the secondary oxidant gas to the bottom of said tunnel (1), the (said) tube (s) (9) being oriented (s) so that said oxidant gas is directed in jet towards the sting, - at least one tubing (10) to bring the toxic gaseous effLuent to the bottom of said tunnel (1), The (the) said (s) tubing (s) ⁽ 10 ⁾ being oriented ( s) so that the effLuent is directed in a jet (s) converging towards the axis (D) of the dart, - a gas extraction device creating a vacuum in said tunnel (1). 10. InstaLLation according to claim 9, characterized in that (The) said (s) tubing (s) (9) bringing the secondary oxidizing gas has (have) a slit shape. 11. InstaLLation according to one of claims 9 or 10, characterized in that it comprises at least two tubes (9) to supply the secondary oxidizing gas, one being reserved for the fixed jet. The other with a modular jet. 12. Installation according to one of claims 9 to 11, characterized in that the combustion tunnel (1) is extended by a post-combustion zone (2) whose axis makes an angle with that (D) of said tunneL (1), said zone (2) being provided at its bottom with a lining of refractory materials (14). 13. InstaLLation according to claim 12, characterized in that a valve (17) is arranged in the top of the post-combustion zone (2).